Catalytic dehydrogenation of hydrocarbons



Patented July 1947' CATALYTIC DEHYDROGENATION OF HYDROCARBONS i John 0.Smith, in, Crani'ord, N. J. assig'nor to t N. J a corporation ofDelaware Tide Water Associated Oil Company, Bayonne,

No Drawing. Application A r-n 2, 1942, j

Serial No. 437.411

3' Claims. (01. zoo-cos) The present invention relates to reactionsinvolving catalytic conversion of aliphatic and alicyclic hydrocarbons;and more particularly to a method for the production of cyclichydrocar-, bons from hydrocarbons containing straight,

chains of at least six carbon atoms by dehydrogenation reactions. Theinvention has special application in the dehydrogenation of naphthenesand the dehydrogenation and cyclization of straight chain parafiins toproduce aromatics. The method of this invention'may be applied tohydrocarbon materials as purecompounds or, to

hydrocarbon mixtures. Also included in the in-.

vention is a catalyst composition effective for in said methods andreactions.

It is known that certain hydrocarbons, particularly those occurring ingasoline fractions and other petroleum fractions, can be aromatized byreactions involving dehydrogenation. For example, hydrocarbons occurringin certain naphthas, such as cyclohexane and methyl cyclohexane,parafiins with straight chains of six or more carbon atoms,cyclopentanes with one or more carbon atoms in aside chain when treatedin pure form or in mixtures under proper condiuse tions may bearomatized with evolution of hydrogen gas. Aromatics are produced invarious refining operations, particularly in cracking methods in whichaliphatic hydrocarbons are subjected to intensive thermal cracking.However, the yields of aromatics resulting from such methods have beengenerally small and because of this and other difiiculties resort hasbeen made to aromatization reactions involving use or catalysts. Ingeneral the catalysts employed have been certain oxides of metals. r fDespite the large number of catalysts heretofore proposed for this and.other purposes,'the art has developed mainly. inempirical manner due tothe diiiiculties usually encountered in catalytic research of reasoningby analogy. A given catalyst efl'ective in one typeof reaction cannot bepredicted with certainty to be eifective in other reactions. Thepresent; invention is concerned with use in dehydrogenation reactions ofa 1 as for example at about 950 F. This treatment.

, nets. of the various carrier materials activated alumina" in granularform is particularly suit able for use with the oxides of thisinvention. Desirably the zirconium oxide is first applied to the aluminafollowed by application of. the molybdenum oxide, but othermodifications are within the scope of the invention. These include thereverse order of'deposition from, that stated as well as alternatesuccessive depositions of the two oxides continueduntil the requiredamounts of each'have been deposited. Deposition of the oxides onthecarrier may be conveniently effected by heating suitable sized granulesof the car rier material with salts of the metals which are decomposabletothe oxides by, heating. More specifically, in preparing a compositecatalyst which will be herein referred to as molybdenum oxide onzirconium oxide on alumina, it has been found desirable to proceed asfollows:

Dissolvein ice water suflicient zirconium tetrachloride to produce onheating the desired proportionate amount of zirconium oxide and mix withalumina particles. The particle size of the alumina mayvary to'suitrequirements. Good results have been obtained using particle sizes of20-40 mesh and 12-14 mesh, but other particle sizes'm'ay be used. Drythe mixture of alu-" mine. and zirconium tetrachloride on a steam bathto remove water. Then add sufficient ammonium molybdate solution toproduce the desired proportionate amount of molybdenum oxide,

mix thoroughly and dry on a steam bath. Then heat the resulting. producton a hot plate to volatilize ammonium chloride, being careful not tooverheat. In this latter step the temperature of the material should notbe allowed to exspecific composite catalyst producing .particularlyadvantageous results in aromatization of hydrocarbons of the type setforth hereinabove.

Stated more specifically, the method of this invention comprises theproduction of aromatic hydrocarbons 'by contacting suitable aliphatichydrocarbons with catalysts comprising oxides of molybdenum andzirconium associated with a carrier or supporting material underconditions conducive to the formation of the desired prodceed about 1400F.

' The composite catalyst so produced may be i'urther treated priorto useby heating in the apparentlycauses conversion to lower oxides of themetals, ,probably toMoOz or M0203 andZrOz;

Alternately instead of reducing the catalyst with hydrogen priorfto usethe reduction may be accomplished in the course ofits use inthe in-'tended aromatization reactions, in which case 2,4a4,ose

. 3 of 950-1000 F. are in general satisfactory. When no more CO: is mentis stopped and the catalyst is ready for preliminary reduction withhydrogen or reuse as stated. Y

By way of specific embodiment, normal heptane was passed in vapor phaseat substantially atmospheric pressure over a catalyst prepared as abovedescribed and consisting of 6% molybdenum oxide on 10% zirconium oxideon Alorco" grade A activated alumina ata temperatureof about 950 F. Ahigh. yield of toluene resulted in the liquids condensed from thereaction which in and a very low proportion of oleflns.

The fact that only relatively small amounts.

of olefins are produced by use of this catalyst is an important featureof the invention since oleflns, probably by entering into sidereactions,-tend to poison the catalyst and reduce its useful lifeas wellas reducing given amount of charging material.

The reaction temperature may be varied from that stated hereinabove. Theoperating temperature in any case must be high enough to eifect thedesired reaction and while a specific lower temperature limit naturallycannot be set with arithmetical precision, temperatures below about 700F. do not give useful results. With charging stocks predominantlystraight chain in character the lowest useful temperature is about 800'F. Likewise, a precise upper temperature limit holding for all casescannot be stated since this factor varies. with other conditions andwith different charging stocks. The upper depends largely upon the rateof cracking occurring with the particular charging stoc and spacevelocity or contact time used. The yield of aromatics increases with thereaction temperature. Likewise the rate of cracking increases'withtemperature and if too high a temperature is used excessive crackingwill occur, i. e., a temperature will be reached at which the relativerate of cracking will predominate over the formation of aromatics asevidenced by material reduction in aromatic yield due to high conversionof the charge to cracked products. This temperature will usually be inthe neighborhood of 1000' F. It is desirable to operate at temperaturesat which the rate of formation of the desired aromatic By use ofappropriate-charging materials there may be prepared by dehydrogenationor dehydrogenation and cyclization various hydrocarbons, such astoluene, benzene, xylene, and the like.

temperature limitevolved regeneration treatparable aromatizingeffectiveness and low olefin production was obtained using a catalystprepared by depositing first molybdenum oxide and then zirconium oxideon activated alumina, in which the charging material and operatingconditions I for example, the dehydrogenation of cyclohexane addition totoluene contained some iso-paraifins the aromatic yield from a by use ofthe catalyst is accomplished with marked efiectlveness.

In ordinary operation where production of aromatics is the sole or majorconsideration, it is desirable to operate at normal or only moderatelyelevated pressures, but super-atmospheric pressures may be used in somecases in the production 'of special effects or products. when, besidesaromatics, an increased yield of iso-paraflins is also desired, the useoi super-atmospheric pressures on the order of say 1000 to 2000 poundsper.

square inch are beneficial since such pressures favor formation ofiso-paraflins. when employing super-atmospheric pressures the catalystis more rapidly poisoned. Catalyst poisoning may be avoided or reducedby conducting the catalytic conversion in the presence oi hydrogen whichmay be introduced into the catalyst chamber.

- a catalyst comprising molybdenum oxide on zirproducts continues topredominate over the cracking rate.

An important aspect of the invention resides in the aromatization ofspecific petroleum fractions high in seven carbon atom hydrocarbons toproduce therefrom good yields of toluene. Thus, aromatics may beeffectively produced by the method of the invention using as chargingstock Thus, it will be apparent that operating conditions may be variedwithin the scope of the invention, depending upon the results desired.

I I claim: p

1. Method for dehydrogenatlng aliphatic hydrocarbons which comprisescontacting said hydrocarbon under dehydrogenating conditions with coniumoxide on alumina.

.2. Method for dehydrogenating aliphatic hydrocarbons which comprisescontacting said hydrocarbons under dehydrogenating conditions with acatalyst comprising about six per cent molybdenum oxide and about tenper cent zirconlum oxide.

3. Method for dehydrogenatingaliphatic hydrocarbons which comprisescontacting said-hydrocarbons under dehydrogenating conditions with acatalyst comprising zirconium oxide on molybdenum oxide on alumina.

JOHN 0. SMITH, Ja.

REFERENCES crrrzn The following references are of record in the file oithis patent;

pub.- by The Aluminum Ore 00.,- East St. Louis, Illinois (1938), (46pages, 2 sheets tables). in Division 31.)

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